Resistant keratinocytes in 7,12-dimethylbenz[a]anthracene-initiated hamster buccal pouch epithelium

In order to test the hypothesis that the property of resistance to cytotoxicity is an acquired trait of premalignant oral mucosal epithelium, cell dissociates were prepared from in vivo initiated hamster buccal pouch epithelium (HBPE), non-initiated HBPE and malignant HBPE cell lines. These cell types were evaluated for resistance to the cytotoxic effects of the inducing carcinogen, 7,12-dimethylbenz[a]anthracene (DMBA). A mitoinhibition assay and a clonogenicity assay were used to assess the ability of these cells to replicate or form colonies in the presence of 40 microM DMBA. Replication of primary plated HBPE cells was inhibited by 100% in both assays. PO II, a cell line derived from non-initiated, paraffin-oil-exposed HBPE, was inhibited by 97 and 100% in the mitoinhibition and colony-forming assays respectively. This same cell line, like primary plated HBPE, lacked the transformation-linked traits of angiogenesis and anchorage-independent growth. By contrast, three malignant HBPE cell lines, two derived during long-term culture of DMBA-initiated HBPE, and one from a DMBA-induced HBPE carcinoma, were inhibited by only 34% or less in the assays for resistance to cytotoxicity. Primary cell cultures derived from HBPE initiated in vivo with twice-weekly topical applications of a 0.5% solution of DMBA in paraffin oil, for 3 or 5 weeks, were inhibited to an intermediate degree, indicating the presence of DMBA-resistant cells. In addition, DMBA-resistant cell colonies were observed in cell cultures prepared at 2, 6 and 10 weeks after completing the 5 week initiation regimen. Progenitors of the resistant cells, persisting in vivo for several weeks after initiation, may represent early preneoplastic cell populations in this experimental model.